Faqi Yu

Flower-to-petal structural conversion and enhanced interfacial storage capability of hydrothermally crystallized MnCO3via the in situ mixing of graphene oxide

Graphene oxide (GO) possesses high electron conductivity and good chemical-binding ability and thus can be used as a multifunctional additive for the preparation and application of electrode materials. As for the hydrothermal crystallization of MnCO3 herein, the absence of GO causes the formation of MnCO3 flower-like architectures composed of secondary spindles, while the presence of GO induces the flower-to-petal structural conversion and results in MnCO3 spindle–GO composites. When applied as Li-ion battery anodes, the composite electrode delivers an initial coulombic efficiency (CE) of 71% and a reversible capacity of 1474 mA h g−1 in the 400th cycle, much higher than those of MnCO3 flowers (the initial CE ∼ 58%, the 400th capacity ∼ 1095 mA h g−1) operated under the same conditions. In particular, the combination of discharging behavior and its differential capacity profile has been successfully used to estimate the interfacial contribution fraction (42%) of the whole reversible capacity (i.e., 1474 mA h g−1) enhanced by the in situ mixing of 8.3 wt% GO.

The controlled synthesis and improved electrochemical cyclability of Mn-doped α-Fe2O3 hollow porous quadrangular prisms as lithium-ion battery anodes

A two-step process of initial oxalate co-precipitation and subsequent thermal decomposition facilitates the formation of hydrated oxalate precursors with hollow quadrangular prism shapes, and then confers a porous nature for the prismatic shells of synthetic hematite (α-Fe2O3) and its Mn-doped derivative. When applied as lithium-ion battery anodes, Mn-doped α-Fe2O3 exhibits an improved electrochemical performance compared with undoped α-Fe2O3. At a current density of 200 mA g−1, the pure α-Fe2O3 electrode gives an initial discharge capacity of ∼1280 mA h g−1 with a low retention ratio of 13.9% (i.e., capacity ∼ 178 mA h g−1) over 80 cycles, while the Mn-doped product, rhombohedral Fe1.7Mn0.3O3, delivers a relatively low initial value of ∼1190 mA h g−1 and retains an 80th cycle reversible capacity of ∼1000 mA h g−1 (i.e., retention ratio ∼ 84.0%). These, together with the better high-rate capability and the lower charge-transfer resistance of the Mn-doped α-Fe2O3 anode, simultaneously demonstrate a successful mass production of hollow porous configurations and an effective doping with elemental Mn for potential application.